The correct answer is c) 4.99 x 10^23 photons

Explanation:

The energy of a photon is given as E = hf

where,
h = Planck’s constant = 6.626×10^-34 Js
f = frequency = c/x
c = speed of light = 3×10^8 m/s
x = wavelength = 525 nm = 525×10^-9 m

E = hc/x
=> E = 6.626×10^-34 × 3×10^8 / (525×10^-9)
=> E = 3.79×10^-19 J/Photon
=> E = 3.79×10^-22 kJ/Photon

And, 189 kJ/3.79×10^-22 kJ/photon = 4.99×10^23 photons.

So the number of photons is 4.99×10^23 photons.